Proximity sensing technology has become popular across a wide range of industries, especially in consumer electronics. The largest applications for proximity sensors within consumer electronics are smartphones, tablets and other mobile devices. These devices are referred to herein as user devices.
The proximity sensing is done for several purposes, some of which may include: (1) reduce display power consumption by turning it off when holding a user device near a human body, (2) disable the touch screen to avoid inadvertent touches by a human body when holding a user device near it and (3) reduce transmit power of a user device to reduce the Specific Absorption Rate (SAR). The SAR is a measure of the rate at which energy is absorbed by a human body when exposed to a Radio Frequency (RF) electromagnetic field. The Federal Communications Commission (FCC) and other regulatory agencies require electronic devices to reduce the RF transmit power of a user device when in close proximity to a human body to keep SAR at or below allowed levels.
The capabilities of a user device may vary widely depending on the type of device. For example, a user device may have a capability to communicate with a mobile wireless network based on different radio access technologies (RAT) such as Long Term Evolution (LTE) from the 3rd Generation Partnership Project (3GPP), or Code Division Multiple Access (CDMA) from 3rd Generation Partnership Project-2 (3GPP2), or Wideband CDMA (WCDMA) from 3GPP, or Global System for Mobile Communications (GSM) from 3GPP, etc. The mobile wireless networks based on these technologies are referred to herein as Wireless Wide-Area Networks (WWAN). A user device may include a WWAN modem for one or more RATs. For example, a user device may include modems for 3GPP LTE and 3GPP WCDMA RATs. A high level block diagram of a portion of a generic user device 100 with WWAN support is shown in FIG. 1. It comprises a display 102, a keypad 104, an RF and baseband (BB) receiver 106 for WWAN, an RF and BB transmitter 108 for WWAN. The RF and BB receiver 106 and RF and BB transmitter 108 for WWAN are together referred to herein as WWAN modem 110. The user device 100 also comprises a Central Processing Unit (CPU) 112 for overall control of the device. The user device 100 also comprises the proximity sensor 114, the Proximity Sensor Control Unit 116, and the SAR Control Unit 118. The Proximity Sensor Control Unit may perform proximity detection by controlling the proximity sensor, making measurements and outputting proximity detection results. The SAR Control Unit accepts the inputs from Proximity Sensor Control Unit and determines whether any reduction in RF transmit power is required.
A user device may support communication over a Wireless Local Area Networks (WLAN). One of the most commonly used WLAN technology is based on the IEEE 802.11 standards and it is also commonly known as Wi-Fi. The terms WLAN and Wi-Fi may be used interchangeably herein. A high level block diagram of a portion of a generic user device 200 with WLAN support is shown in FIG. 2. The user device 200 comprises an RF and BB receiver 202 for WLAN, an RF and BB transmitter 204 for WLAN. The RF and BB receiver 202 and RF and BB transmitter 204 for WLAN are together referred to herein as WLAN modem 206. The user device 200 also comprises a CPU 208 for overall control of the device. The maximum RF transmit power for Wi-Fi may be up to 20 dBm as per FCC regulations. It may vary depending on regional regulatory requirements.
A user device may support wireless link over a Bluetooth protocol for communicating with other devices in a Personal Area Network (PAN). A high level block diagram of a portion of a generic user device 300 with Bluetooth support is shown in FIG. 3. The user device 300 comprises an RF and BB receiver 302 for Bluetooth, an RF and BB transmitter 304 for Bluetooth. The RF and BB receiver 302 and RF and BB transmitter 304 for Bluetooth are together referred to herein as Bluetooth modem 306. The user device 300 also comprises a CPU 308 for overall control of the device. Bluetooth may be classified as Class-1, Class-2 or Class-3 with maximum RF transmitter power of 20 dBm, 4 dBm, and 0 dBm respectively.
The maximum RF transmit power of modems for some radio access technologies may not be high enough to require any RF power reduction to meet SAR requirements. For example, Class-2 and Class-3 Bluetooth devices have very low maximum RF transmit power and therefore SAR requirements can be met without any RF power reduction. In such cases, there may not be a need for user proximity detection. The maximum RF transmit power of modems for some radio access technologies may be high enough to require RF power reduction to meet SAR requirements. For example, the maximum RF transmit power for a user device in a 3GPP LTE WWAN system is 23 dBm and in a GSM system is 33 dBm.
When a user device is performing a particular activity it may be described as being in a particular state. For example, when a user device is actively performing data transfer with a network, it may be considered to be in Active state. For the purpose of proximity detection and SAR control, an Active state may also be defined as a state whenever RF Transmitter of a WWAN modem or a WLAN modem is on. Similarly, when a user device is not performing any data transfer with a network and not performing any other activity, it may be considered to be in Idle state. A user device may be in some other intermediate state depending on a particular scenario. Similarly, different subsystems of a user device may be in different states. For example, the WWAN modem may be in Active state or Idle state. Similarly, a WLAN modem, a Bluetooth modem, or a proximity sensor subsystem may be in Active or Idle state. The specific names used for the states for different subsystems may vary but the general idea remains the same. The power consumption of a subsystem may be different depending on the state it is in.
Different parts of a user device may be in different states depending on the prevailing scenario. For example, when a user device with WWAN modem in FIG. 2 is not performing any active data transfer over WWAN, the WWAN modem may be in Idle state. When a user device is performing active data transfer over WWAN, the WWAN modem may be in Active state. Similarly, when a proximity sensor is powered on and actively scanning for possible presence of a user nearby, it may be in Active state. Otherwise, it may be in Idle state. In Idle state of the proximity sensor, the power supply to it may be disabled.
In a conventional user device, the SAR control may be fixed based on the RF transmit power levels of the modem in the user device.